Polymer hydrogenation process

ABSTRACT

A process for hydrogenating unsaturations in polymers, the process comprising contacting at least one polymer having unsaturations with a catalyst comprising at least one Group Ia, Ib, IIb, VIb, VIIb or VIII metal on a support of an alkaline earth metal silicate having a surface area of at least 30 m2/g at a temperature of from 50 to 250° C. and a pressure of from 5 to 150 bar.

The present invention relates to a process for hydrogenating unsaturatedpolymers, in particular a process for the selective hydrogenation ofstyrene-butadiene-styrene copolymers with high selectivity towardshydrogenation of the ethylenically (olefinic) unsaturated regions with aminimal amount of hydrogenation of aromatic unsaturated regions.

Styrene-butadiene-styrene (SBS) copolymer is produced by means of“living ionic polymerisation” which produces block copolymers consistingof a block of polystyrene, following by a block of polybutadiene andterminated by a further block of polystyrene. In the polybutadieneblock, a double bond remains in every butadiene unit. Depending on theinsertion mechanism, two geometrical isomers of the butadiene unit canbe achieved, namely a 1,4 insertion gives a vinylene bond, which may becis or trans, while a 1,2 insertion gives a vinyl bond. The remainingdouble bonds are reactive and limit the stability of the elastomer. Toimprove this, it is known in the art that the butadiene units of thecopolymer can be hydrogenated, giving a block copolymer ofpolystyrene-poly(ethylene-co-butylene)-polystyrene (SEBS). Homogenouscatalysts have been widely used as it has been generally thought in theart that those catalysts can best access the double bonds in thecopolymer chains. The most widely accepted catalysts are based onZiegler-type hydrogenation catalysts, for example nickel salts activatedwith alkyl-aluminium compounds. A major disadvantage of such catalystsis that they have to be removed from the copolymer due to their possiblepoisoning and colouration effects.

It has also been known to use heterogeneous catalysts for hydrogenationof SBS.

For example, EP-A-0378104 discloses polymer hydrogenation catalysts foruse in hydrogenating ethylenically unsaturated regions with a minimalamount of aromatic unsaturation hydrogenation, for example in SBScopolymers. The catalyst is a heterogeneous catalyst comprising a GroupVIII metal and a porous support wherein the porous support ischaracterised by a pore size distribution such that at least 95% of thepore volume is defined by pores having diameters greater than 45 nm andthe ratio of metal surface area to carrier surface area is in the rangeof from 0.07 to 0.75:1. The catalyst is very active under mildtemperature conditions, from room temperature to 140° C. The Group VIIImetal may be selected from at least one of palladium, rhodium,ruthenium, cobalt, nickel and platinum on a porous, powdery or granularcarrier or support material such as diatomaceous earth, alumina,activated carbon, silica-alumina or silica. The specification emphasisesthe requirement of exceptionally large pores even with low surface areaand pore volume of the support.

WO-A-94/21694 discloses a method for hydrogenation of polyolefin(alkenyl aromatic) polymers or poly(alkenyl aromatic)/polydiene blockcopolymers that provides hydrogenated polymers with 99.5% or greatersaturation and a molecular weight distribution of less than about 3. Themethod comprises contacting the copolymer with a metal catalyst on aGroup I or II metal support. Preferred catalysts are transition metalcatalysts with gold, silver, palladium, platinum, rhenium, nickel,rhodium and chromium being especially preferred. The catalyst support isdisclosed as being any Group I or II metal salt such as lithium, sodium,potassium, barium, calcium, magnesium or cesium salts, preferably bariumor calcium salts, more preferably BaSO₄, CaCO₃ or BaCO₃.

WO-A-96/34896 discloses a process for hydrogenating aromatic polymers inthe presence of a silica supported metal hydrogenation catalyst, thesilica having a pore size distribution such that at least 98 percent ofthe pore volume is defined by pores having a diameter greater than 600angstroms.

U.S. Pat. No. 4,452,951 and its equivalent DE-A-3227650 disclose aprocess for hydrogenating a conjugated diene polymer in the presence ofa hydrogenation catalyst having a porous silica support, the silicahaving an average pore size diameter of from 80 to 1200 angstroms and aspecific surface area of not more than 600 square metres per gram.

U.S. Pat. No. 5,155,084 discloses supported catalysts containing nickel,magnesium oxide and, if desired, further additives, which containreduced Mg and Ni in a molar ratio of (0.0075 to 0.075):1. The catalystsalso have an active nickel metal surface area of 110 to 180 squaremetres per gram of Ni and a BET total surface area of 160 to 450 squaremetres per gram. Suitable supports are various water-insolublematerials, including silicates, such as calcium silicates, magnesiumsilicates and/or aluminium silicates; alumina; silica and/or kieselguhr.The catalysts may be used for the hydrogenation of aliphatic and/oraromatic hydrocarbons.

A number of catalysts for selective hydrogenation of unsaturatedhydrocarbons are available commercially. Such catalysts comprise, forexample palladium on an alumina support, palladium on an activatedcarbon support, nickel tungsten on an alumina support and palladium on abarium sulphate support. Such catalysts suffer from the technicaldisadvantage of a low activity towards ethylenically unsaturatedpolymers, in other words with a relatively low hydrogenation of the cisand trans ethylenic unsaturations, and of the vinyl unsaturations.

A huge variety of naturally occurring and synthetically producedsilicates are known in the art.

U.S. Pat. No. 3,729,429 discloses layered complex metal silicatecompositions, especially chrysotiles, and their preparation.

U.S. Pat. No. 3,806,585 discloses the production of a hydrous calciumsilicate composed preponderantly of xonotlite in the shape of rodcrystals which is described as having outstanding refractory properties,whereby moulded bodies comprised primarily of xonotlite provide strengthunattained by other inorganic materials. The specification disclosesthat hydrous calcium silicate of the xonotlite type has use inconstruction as a fire proof coating material, as a fire proof moistureretaining material and as a potential filler for plastics and rubberproducts.

U.S. Pat. No. 3,804,652 discloses a method of producing calcium silicateproducts, such as drain pipes and insulating material, to formtobermorite having the empirical formula 5CaO.6SiO₂.5H₂O.

U.S. Pat. No. 3,928,539 discloses a method of producing hydrous calciumsilicates such as xonotlite, tobermorite and the like.

U.S. Pat. No. 3,915,725 discloses a process for producing hollowspherical aggregates of xonotlite, which aggregates are employed to formshaped articles.

U.S. Pat. No. 4,298,386 discloses the production of globular secondaryparticles of the woolastonite group of calcium silicate crystals,including woolastonite and xonotlite.

U.S. Pat. No. 4,689,315 discloses the production of amorphous,approximately spherical silica particles obtained by the acidichydrolysis of an approximately spherical synthetic calcium silicate. Theresultant silica particles, obtained by such acid hydrolysis, aredisclosed as being particularly suitable for use as catalyst support.The starting material may comprise spherical synthetic calcium silicatessuch as xonotlite, tobermorite and/or calcium silicate hydrate, whichare then treated with an aqueous acid having a pH of from 0.6 to 3 toproduce the resultant silica particles for use as a catalyst support.

U.S. Pat. No. 4,849,195 discloses synthetic substantially sphericalcrystal aggregates of xonotlite. The aggregates can be mixed with inertparticles, for example to produce thermal insulation products.Alternatively, as for U.S. Pat. No. 4,689,315 described above, theaggregates of xonotlite can be used as starting material for acidextraction of calcium atoms in order to obtain silica.

The present invention aims to provide an improved method of selectivelyhydrogenating unsaturated polymers.

Accordingly, the present invention provides a process for hydrogenatingunsaturations in polymers, the process comprising contacting at leastone polymer having unsaturations and hydrogen with a catalyst comprisingat least one Group Ia, Ib, IIb, VIIb, VIIb or VIII metal on a support ofan alkaline earth metal silicate having a surface area of at least 30m²/g at a temperature of from 50 to 250° C. and a pressure of from 5 to150 bar.

The present invention is at least partly predicated on the surprisingdiscovery that a basic hydrated crystalline calcium silicate when usedas a catalyst support can yield hydrogenation catalysts having highactivity and selectivity. This is all the more surprising sincexonotlite-type materials have been known for a number of years but tothe applicant's knowledge there has been no disclosure or suggestion inthe prior art of using xonotlite-type materials as catalysts or catalystcarriers. Rather, as disclosed in for example U.S. Pat. No. 4,689,315 asdiscussed above, xonotlite has been proposed in the prior art for use asa starting material for the production of silica, where the chemicalcomposition and structure of the xonotlite is destroyed in thepreparation of the silica particles by acid hydrolysis.

Preferred embodiments of the present invention will now be described ingreater detail by way of example only.

The hydrogenation catalyst of the present invention preferably comprisesa supported noble metal catalyst.

The hydrogenation catalyst of the present invention comprises at leastone Group Ia, Ib, IIb, VIIb, VIIb or VIII metal, such as Pd, Co, Rh, Ru,Ni, Mo, W, Fe, Cu, Na or K or a combination thereof with palladium beingparticularly preferred.

The metal or metals may be in the metallic state, in an oxidic state, ina partially reduced oxide state, or in a sulphided or partiallysulphided state. Optionally, bi-metallic metals or bi-metallic compoundsmay be incorporated into the hydrogenation catalyst, such as CoMo, NiW,and NiMo sulphided catalyst for hydro-treatment and, for selectivehydrogenation, Cu—Pd, Cu—Ni, Cu—Co, Cu—Pt, Fe—Pd, Co—Pd, Ni—Pd, Pt—Pd,Ag—Pd, Fe—Pt, Ni—Pt, Pt—Sn, Pt—Pb, Pd—Sn, Pd—Pb and Au—Pd.

The preferred catalyst support is a basic alkaline earth metal silicatewith a very open and accessible pore structure. A most preferredcatalyst support comprises a synthetic crystalline hydrated calciumsilicate having a chemical composition of Ca₆ Si₆ O₁₇ (OH)₂ whichcorresponds to the known mineral xonotlite (having a molecular formula6CaO.6SiO₂.H₂O). The catalyst support preferably has a sphericalmorphology with a mean diameter of the spherical particles being from 10to 200 μm. The support has a very open structure comprising an outershell with a very close-crystal structure surrounding an open innerstructure. This may be referred to as an egg shell like structure. Theouter shell is formed of interlocked ribbon-shaped crystals yieldingregular and homogeneous surface properties. The outer shell is providedwith pore openings up to 2000 Angstroms, more preferably from 100 to1000 Angstroms, in diameter. This provides a good pore structure withhigh pore volume.

Preferably, the support has a specific surface area well above 10 m²/g,ranging from 30 to 200 m²/g, more preferably from 40 to 90 m²/g.

The support material is preferably pH basic. More preferably, thesupport material has a minimum basicity corresponding to a pH of greaterthan 7.5. The pH may be measured when 4 wt % of the support material isimmersed in water.

Generally, a synthetic hydrated calcium silicate is synthesisedhydrothermally under autogeneous pressure. A particularly preferredsynthetic hydrated calcium silicate is available in commerce from thecompany Promat of Ratingen in Germany under the trade name Promaxon D.This material exhibits some basicity due to the presence of calcium, andin a 4% by weight dispersion in water, the pH reaches a value of around10. The specific composition of the preferred synthetic hydrated calciumsilicate is specified in Table 1.

In order to demonstrate the thermal stability of xonotlite, andtherefore the applicability of xonotlite as a carrier for hightemperature reactions, commercial xonotlite sold under the trade namePromaxon D was calcined in ambient air at a relative humidity of about50% at two different temperatures, namely 650° C. and 750° C., each fora period of 24 hours. The initial xonotlite had a crystalline phaseCa₆Si₆O₁₇(OH)₂ with a BET surface area of 51 m²/gram and a pore volume(of less than 100 nanometers) of 0.35 ml/gram. After calcination at 650°C., the carrier retained its crystallinity which corresponds to that ofxonotlite. Thus after a 24 hour calcination at 650° C., the crystallinephase still comprised xonotlite (Ca₆Si₆O₁₇(OH)₂) with a BET surface areaof 47.4 m²/gram and a pore volume (less than 100 nanometers) of 0.30ml/gram. After the calcination at 750° C., the carrier was transformedinto wollastonite (having the crystalline phase CaSiO₃) by losing onewater molecule. This made the carrier less basic. Furthermore, as aresult of calcination at 750° C. the carrier lost much of its porevolume, being reduced to 0.09 ml/gram (for pore sizes of less than 100nanometers) and the BET surface area was correspondingly reduced to 38m²/gram.

These results show that xonotlite has utility as a basic carrier forhigh temperature reactions in the range of up to 650° C. In thistemperature range the xonotlite retains its basicity, resulting in thecarrier being suitable for incorporation in a catalyst for use in hightemperature reactions.

The at least one Group Ia, Ib, IIb, VIIb, VIIb or VIII metal ispreferably present in an amount of from 0.01 to 10 wt %, more preferablyabout 0.5 wt %, based on the weight of the supported catalyst.

The catalyst is produced by impregnating the at least one Group Ia, Ib,IIb, VIIb, VIIb or VIII metal on the alkaline earth metal silicatesupport. Preferably, an incipient wetness impregnation technique isemployed where the pores of the support are filled with a volume ofsolution containing the metal. In this technique, the dried catalyst isimpregnated with a solution of a salt of the at least one Group Ia, Ib,IIb, VIIb, VIIb or VIII metal, for example a halide of the metal, inparticular the Group VIII metal chloride. The amount of the metal saltis calculated to provide a desired metal content on the support, forexample a metal content of from 0.01 to 10 wt % based on the weight ofthe supported catalyst, most preferably about 0.5 wt % based on theweight of the supported catalyst. The impregnated solid is dried firstunder vacuum and subsequently at elevated temperature. Finally, theproduct is calcined, for example at a temperature of about 250° C. for aperiod of about 3 hours.

Alternatively an excess of solution is used during the impregnation stepand the solvent is removed by evaporation. Depending on the propertiesof the impregnation solution and the carrier the active metal phase canhave different locations: (1) the metal or metal compound isconcentrated in a thin layer close to the external surface, this may bereferred to as an “egg-shell mode”, (2) the metal or metal compound isconcentrated in a thin layer below the surface, but not penetrating tothe centre, this may be referred to as an “egg-white mode”, (3) themetal or metal compound is concentrated in a small zone near the centreof the particle carrier, this may be referred to as an “egg-yolk mode”,and (4) the metal or metal compound is uniformly distributed throughoutthe particle carrier. The way that the metal precursor will interactwith the carrier depends on the isoelectric point (IEP) which is the pHat which the particle of the carrier in an aqueous solution has no netcharge. At pH's above the IEP, cations will be adsorbed, because thesurface carries a negative charge; below the IEP, only anions will beadsorbed, because the surface carries a positive charge. During thecontact of the impregnating solution and the carrier, ion exchange canalso occur. The impregnating solution may be altered by addingcomplexing agents, which can change the charge of the metal precursor.In another technique, competing ions may be added to improve thespreading of the metal precursor over the carrier.

In alternative embodiments of the catalyst production process, the metalmay be deposited on the support by ion exchange or vapour phasedeposition.

The feedstocks to be selectively hydrogenated comprise unsaturatedcopolymers with both ethylenic and aromatic unsaturated regions. Themost preferred feedstock comprises an SBS block copolymer, butalternative feedstocks include polyethylene (PE), polypropylene (PP),polybutene (PB), ethylene propylene rubber (EPR), ethylene propylenediene monomer (EPDM), polybutadiene (PB), styrene-butadiene rubbers,polydienes, petroleum resins, synthetic resins, synthetic lubricantslike ethylene-propylene co-oligomers and polyalphaolefins.

The catalyst of the present invention is a heterogeneous catalyst whichmay be used in a batch wise or continuous process. Preferably, thecatalyst is used in a fixed bed reactor. A most preferred processemploys a continuously operated fixed bed reactor. The unsaturatedpolymers to be hydrogenated preferably comprisestyrene-butadiene-styrene copolymers in solution in a solvent, forexample cyclohexane, optionally with a minor amount of tetrahydrofuran(THF), an aromatic such as benzene, toluene or xylene, naphtha,kerosene, and liquefied hydrocarbons, such as C₃'s, C₄'s etc.

Typically, the SBS copolymer is present in an amount of from 1 to 75% byweight in the solvent, more preferably around 10% by weight.

In the hydrogenation process, the SBS copolymer in solution is contactedbatch-wise or continuously passed over the catalyst at elevatedtemperature and elevated pressure. Typically, the temperature is from 60to 200° C., more preferably from 100 to 160° C., and most preferablyaround 120° C. The total pressure is preferably from 5 to 150 bar, morepreferably from 20 to 100 bar, most preferably around 60 bar. Thehydrogen/aliphatic unsaturation molar ratio is preferably from 2 to 200.The SBS copolymer feed is preferably contacted with the catalyst for aperiod of from 0.1 to 100 hours, more preferably from 10 to 35 hours ina batchwise hydrogenation. In a continuous hydrogenation the contacttime is between 0.1 to 10 litres of solution per litre of catalyst perhour, most preferred about 1 h⁻¹.

When hydrogenating unsaturated polymers containing both ethylenicallyunsaturated regions, for example in the butadiene units of the SBScopolymer, and also aromatic unsaturated regions, for example in thestyrene units of the SBS copolymer, the present inventors have foundthat by using a pH basic catalyst support in conjunction with a catalystsupport having large surface area and large pores giving highaccessibility and also in combination with low hydrogenation temperatureand high hydrogenation pressure, a high selectivity toward hydrogenationof the ethylenically unsaturated regions with a minimal amount ofaromatic unsaturation hydrogenation is achieved.

The use of a heterogeneous catalyst in accordance with the inventionprovides an advantage over homogeneous catalysts that the catalyst caneasily be removed from the polymer following the hydrogenation process.

The present invention will now be described with reference to thefollowing non-limiting examples.

The Examples were performed on a laboratory-scale batch-wise benchreactor, where the contact period between the catalyst and the polymerwas measured. However, in commercial production it is envisaged that thereaction would be continuous, in which case the polymer feedstock wouldbe fed over the catalyst at an liquid hourly space velocity (LHSV),typically of from 0.1 to 50 h⁻¹.

EXAMPLE 1

Catalyst Preparation

A sample of the hydrated crystalline calcium silicate available incommerce under the Trade name Promaxon D was dried at a temperature of500° C. for a period of 3 hours. The dried support was then impregnatedwith a solution of palladium chloride (PdCl₂) using a wet impregnationtechnique. In particular, 100 g of dried Promaxon D were progressivelycontacted with 46.4 g of an aqueous palladium chloride solution, theamount of solution being selected so as to correspond to the estimatedabsorption capacity of the dried Promaxon D. The amount of the palladiumsalt was calculated in order to reach a final palladium content in theresultant catalyst of 0.5 wt %. The impregnated solid was dried undervacuum for a period of 6 hours at 25° C. and thereafter dried for aperiod of 16 hours at a temperature of 110° C. After the dryingtreatment, the loss on ignition of the resultant catalyst, at atemperature of 500° C. for a period of 1 hour, was around 2.3 wt %.Finally, the catalyst was calcined at a temperature of 250° C. for aperiod of 3 hours. The powder catalyst was then pelletised. The catalystwas then introduced into a quartz tubular reactor and purged at roomtemperature (25° C.) under nitrogen. The temperature was then increasedup to 100° C. and nitrogen was replaced by hydrogen. The catalyst wasthen activated under hydrogen at a temperature of 110° C. for a periodof 16 hours. The activated catalyst was kept under nitrogen.

EXAMPLE 2

Hydrogenation of SBS Copolymers

An amount of 10 g of the activated catalyst described in Example 1 wastransferred under nitrogen into a Parr reactor having a volume of 2litres with 500 g of an SBS rubber solution in cyclohexane. The SBS is ablock copolymer consisting of PS-PB-PS where PS is polystyrene and PB ispolybutadiene. The rubber solution had a total SBS content of 16.8 wt %,a Bookfield viscosity at 25° C. of 780 cps, a THF concentration of 60ppm and no antioxidant. In the SBS copolymer, gel phase chromatography(GPC) yielded a Mp of 76,000 Daltons. The rubber had a total styrenecontent of 30.9 wt % and the microstructure of the polybutadiene blockcomprised vinyl bonds 9.6 wt %, trans vinylene bonds 53.7 wt % and cisvinylene bonds 36.7 wt %. The styrene content and the microstructure ofthe polybutadiene block were determined by infrared analysis done on thedry rubber, after addition of an antioxidant system.

After a leak test with nitrogen, the reactor was then pressurised withhydrogen to an initial pressure of 15 bar. Then the temperature andpressure were progressively increased to a temperature of 170° C. and ahydrogen pressure of 35 bar. The hydrogenation was carried out for aperiod of 16 hours.

After the hydrogenation process, the SBS solution became cloudy, whichwas believed to be due to the low vinyl portion of the polybutadieneblock. The resultant polyethylene block tended to reticulate. Theresultant hydrogenated SBS copolymer was analysed by ¹H-NMR, with theconversion of the olefinic region being based on the assumption that thestyrene content remained constant. The degree of the cis and transconversion, and of the vinyl conversion, are specified in Table 2.

It may be seen that the catalyst of Example 1 exhibited high conversionlevels of the olefinic region which was believed to be due to theaccessible active sites in the catalyst support which in turn werebelieved to be due to the open structure of the catalyst support whichwas readily accessible by the copolymer molecules and due to the basicnature of the catalyst support.

COMPARATIVE EXAMPLES 1 TO 4

In these Comparative Examples, various hydrogenation catalysts wereemployed to hydrogenate the same SBS copolymer under substantially thesame conditions as for Example 1. The catalysts of Comparative Examples1 to 4 comprised, respectively, palladium on barium sulphate (availablefrom Janssen Chemicals of Belgium under the reference 19,506,09), nickeltungsten on alumina (available from Procatalyse of France under thereference LD 155), palladium on activated carbon (available fromEngelhard of the Netherlands under the reference 3234/B) and palladiumon alumina (available from Sud Chimie of Germany under the referenceG68C-1). The results are also shown in Table 2. For Comparative Examples1, 2 and 3, the hydrogenation was performed in two stages at varyingtemperatures and pressures for different periods of time. ForComparative Example 1, the powder catalyst was pelletised before use,whereas for Comparative Examples 2 to 4 the catalysts were used in theas-received form. The nickel tungsten/alumina catalyst of ComparativeExample 2 was additionally sulphurised with dimethyl disulphide (DMDS)in naphtha. In Comparative Example 1 the conversion of the ethylenicallyunsaturated regions was determined by infra-red analysis rather than¹H-NMR.

It may be seen from a comparison of the conversion levels of ComparativeExamples 1 to 4 and Example 1 that the conversion levels of theethylenically unsaturated regions is higher for Example 1 than forComparative Examples 1 to 4. The nickel tungsten/alumina andpalladium/activated carbon catalysts of Comparative Examples 2 and 3exhibited the lowest hydrogenation activity.

EXAMPLE 3

In this Example, the catalyst produced in accordance with Example 1 wasemployed to hydrogenate a SBS feedstock which had been produced withoutany antioxidant and had been stored under nitrogen. The rubber containeda greater proportion of vinyl bonds than the rubber of Example 2 which,after hydrogenation, resulted in a polyethylene-co-butylene polymerwhich does not reticulate.

The feedstock had a THF concentration of 5000 ppm in solutioncyclohexane. The styrene content was 32% by weight and thevinyl/polybutadiene sequence was 33.8% by weight, both determined ininfra-red spectroscopy. The value of Mp of the final SBS as determinedby gel phase chromatography was 77,700 Daltons. Following evaporation ofthe solvent by an infra-red lamp, it was determined by that the solidscontent in the cyclohexane was 12.4 wt %. The living polymer had beenproduced using an organolithium initiator, using propylene oxide as theterminator. NMR analysis on the solid yielded a styrene content of 32.2wt %, a combined cis vinylene and trans vinylene content of 43.8 wt %and a vinyl content of 24.0 wt %.

The SBS copolymer was subjected to hydrogenation using substantially thesame technique as employed in Example 2 and the results are shown inTable 3.

It may be seen that for a hydrogenation temperature of 120° C. and atotal pressure of 60 bar, a high conversion rate of the ethylenicallyunsaturated region was achieved with a minimal amount of aromaticunsaturation hydrogenation. At least 98% of the vinyl groups arehydrogenated to achieve the desired degree of hydrogenation.

At a hydrogenation temperature of 170° C. and a pressure of 35 bar, thevinyl bond hydrogenation was found to be accompanied by thehydrogenation of a significant amount of the aromatic ring. When thefeedstock was diluted with further cyclohexane in the ratio 1:1,complete removal of the vinyl bond was achieved in a shorter timeperiod, but the hydrogenation also becomes more aselective since morearomatic rings were converted for the same degree of vinylhydrogenation.

For a pressure of 35 bar, the hydrogenation was performed attemperatures of 150, 160 and 170 and 180° C. The results are also shownin Table 4. By increasing the temperature, the conversion rate wasincreased but the vinyl hydrogenation tended to become less selective.

When the reactor pressure was increased to a value of 60 bar, it wasagain found that increasing the temperature increases the conversionrate, but decreases the selectivity of the vinyl hydrogenation. At thepressure of 60 bar, it was found that complete vinyl hydrogenation canbe achieved without significantly affecting the aromatic ring. Thisresult suggested that a rather high pressure is required to convert thevinyl bond to a high extent without hydrogenation of the aromaticnuclei. When working at lower pressure, it is required to increase thereactor temperature to reach an acceptable conversion rate but byincreasing the temperature, the vinyl hydrogenation becomes aselective.Without being bound by theory, it is believed that this is due to ahigher activation energy being required to hydrogenate the aromaticrings, so that at a higher reaction temperature the relative reactionrate (r_(olefins)/r_(aromatics)) decreases leading to a lowerselectivity for olefin hydrogenation. Thus at 120° C. and a pressure of60 bar, the cis and trans double bonds are also completely hydrogenatedwithout any loss of unsaturation in the aromatic rings. The conversionof the cis and trans double bonds is however slower than that of thevinyl groups.

The determination of the conversion of the styrene, cis and transvinylene and vinyl groups was determined by ¹H/NMR analysis usinghexamethyl disiloxane (Me₃Si—O—SiMe₃) as a standard.

TABLE 1 Composition SiO₂ 49.0 wt % CaO 42.9 wt % Al₂O₃ 0.2 wt % MgO 0.3wt % Fe₂O₃ 1.1 wt % Na₂O 0.2 wt % K₂O 0.2 wt % Loss on Ignition 6.1 wt %Specific area (BET) 50 m²/g Bulk Density 90 g/l Average particle size 45μm

TABLE 2 Comparative Comparative Comparative Comparative Example Example1 Example 2 Example 3 Example 4 2 Catalyst Pd/BaSO₄ NiW/Al₂O₃ Pd/CPd/Al₂O₃ Pd/Promaxon D Catalyst weight/gr 7.5 10 10 10 10 SBS weight/gr533 473 518 573 512 Conditions start T/° C. 30 22 26 24 25 H2pressure/bar 30 30 30 30 15 1st T/° C. 150 150 150 170 170 H2pressure/bar 30 30 30 35 35 time/h 0.5 3 2 30 16 2nd T/° C. 150 170 170— — H2 pressure/bar 35 30 35 — — time/h 6 18 20 — — Conversion % Cis &Trans — 8.8 41 81.7 92.4 Vinyl — 55.3 84.4 89.9 100 Cis & Trans & Vinyl20 16.6 48.3 83.1 92.4

TABLE 3 p total % conv % conv % conv T (° C.) t (h) (bar) dilution STC + T Vin 170 1 35 none 0 27 53 170 5 35 none 8 56 88 170 21 35 none 5388 100 170 1 35 1:1cyC6 49 73 85 170 5 35 1:1CyC6 64 92 99 170 10 351:1CyC6 72 95 100 170 21 35 1:1CyC6 97 100 100 150 1 35 none 0 9 2 150 535 none 0 15 20 150 10 35 none 1 35 50 150 21 35 none 1 53 78 160 1 35none 0 35 70 160 5 35 none 0 53 88 160 10 35 none 23 73 98 160 21 35none 67 90 100 180 1 35 none 15 48 79 180 5 35 none 55 81 96 180 21 35none 79 100 100 120 1 60 none 0 1 11 120 5 60 none 3 29 67 120 10 60none 0 40 90 120 21 60 none 0 69 100 120 29 60 none 0 80 100 120 34 60none 0 87 100 120 48 60 none 3 92 100 150 1 60 none 11 62 93 150 5 60none 20 73 98 150 10 60 none 28 81 99 150 21 60 none 76 95 100 190 5 60none 74 91 100 190 10 60 none 97 100 100 190 21 60 none 100 100 100

1. A process for hydrogenating unsaturations in polymers, the processcomprising contacting at least one polymer having unsaturations andhydrogen with a supported catalyst at a temperature of from 5 to 250° C.and a pressure of from 5 to 150 bars, said catalyst comprising at leastone Group Ia, Ib, IIb, VIb, VIIb or VIII metal on a support comprisingcrystalline calcium silicate having a surface area of at least 30 m²/g.2. A process according to claim 1 wherein said support has a surfacearea within the range of 30 to 200 m²/g.
 3. A process according to claim1 wherein said support has a surface area within the range of 40 to 90m²/g.
 4. A process according to claim 1 wherein the calcium silicate hasthe chemical composition Ca₆Si₆O₁₇(OH)₂.
 5. A process according to claim1 wherein the support is in the form of substantially sphericalparticles having a mean diameter of from 10 to 200 microns andcomprising pores in the particles having a diameter of from 100 to 2000Angstroms.
 6. A process according to claim 1 wherein the support has abasicity corresponding to a pH of greater than 7.5 when the support isimmersed in water at a concentration of 4 wt. %.
 7. A process accordingto claim 1 wherein said catalyst comprises palladium impregnated ontothe support in an amount of from 0.01 to 10 wt. % based on the weight ofthe supported catalyst.
 8. A process according to claim 1 wherein saidcatalyst is contacted at a temperature within the range of 100 to 160°C. and a pressure within the range of 20 to 100 bars.
 9. A processaccording to claim 1 wherein said at least one polymer is dissolved in asolvent to provide a feedstock having a solids content of from 1 to 75wt. %.
 10. A process according to claim 1 wherein said at least onepolymer has ethylenically unsaturated regions and aromaticallyunsaturated regions and the ethylenically unsaturated regions areselectively hydrogenated.
 11. A process according to claim 1 whereinsaid at least one polymer comprises a styrene-butadiene-styrenecopolymer.
 12. A process for selectively hydrogenating at least oneunsaturated polymer having ethylenically unsaturated regions andaromatically unsaturated regions comprising contacting said at least onepolymer with hydrogen in the presence of a supported catalyst comprisingat least one Group Ia, Ib, IIb, VIb, VIIb or VIII metal on a crystallinecalcium silicate support having a surface area of at least 30 m²/g, thesupport being in the form of substantially spherical particles andcomprising pores in the particles having a diameter of from 100 to 2000Angstroms.
 13. A process according to claim 12 wherein said pores have adiameter within the range of 100 to 1000 Angstroms.
 14. A processaccording to claim 12, wherein the calcium silicate has the chemicalcomposition Ca₆Si₆O₁₇(OH)₂.
 15. A process according to claim 12 whereinsaid at least one polymer comprises a styrene-butadiene-styrene blockcopolymer.
 16. A process according to claim 15 wherein saidstyrene-butadiene-styrene block copolymer is passed over the catalyst ata temperature within the range of 60-200° C. and a pressure within therange of 5-150 bars.
 17. The process according to claim 16 wherein saidtemperature is within the range of 100-160° C. and said pressure iswithin the range of 20-100 bars.